Linear and Cyclic Amides with a Thiophene Backbone: Ultrasound-Promoted Synthesis and Crystal Structures

A full synthetic study of linear and cyclic thiophene oligoamides has been carried out. The combination of an ultrasonic technique to diminish the intramolecular backfolding of longer oligoamide chains, therefore enhancing the accessibility of the carboxylic acid, and T3P as coupling reagent led to shorter reaction time and higher yields for both linear and cyclic oligoamides. By controlling the degree of dilution, macrocyclic amides with different sizes can selectively be prepared. Different crystal structures of cyclic thiophene oligoamides were also analyzed.